Sheet removal device

ABSTRACT

A sheet removal device for separating an image bearing support sheet from the surface of a heated fuser roll. The removal device is constructed in a configuration and of a material to prevent copy degradation and harming of the fuser roll during the sheet separating operation.

United States Patent 11 1 1111 3,844,252 Thettu Oct. 29, 1974 SHEETREMOVAL DEVICE 447,012 2/1891 Knowlton 61 al. 118 245 1 1 InventRaghulinga Theflu, Webster, 3321331 21138; 5123113351: jiiijjii 13/3321,080,959 12/1913 Eaton 118/262 2,314,051 3/1943 OSgOd.... 118/245 [73]Asslgnee' gel-ox corporat'on Stamford 2,330,530 9/1943 Tuttle 118 101 uxOm 2,360,044 10 1944 Dermody ll8/245 x [22] Filed; May 1973 3,357,401 121967 Wood 118/637 [21] Appl. No; 362,639

Primary ExaminerMorris Kaplan [52] US. Cl 118/60, 34/D1G. 3, 118/70,118/245, 432/ 51 Int. Cl G03g 13/08 [57] ABSTRACT 81 Fleld of Search118/601 A sheet removal device for separating an image bear- 118/104,124, 126, 245, 261, 262, 203, 204; ing support sheet from the surface ofa heated fuser 355/3 15 101/425 429; 34/DIG- 3; roll. The removal deviceis constructed in a configural 17/ 1 NO; 432/6 15/25651; 271/DIG- tionand of a material to prevent copy degradation and 2; 162/1 NO; /1 NO;72/1 NQ harming of the fuser roll during the sheet separating operation.[56] References Cited UNITED STATES PATENTS 15 Claims, 6 Drawing Figures246,728 9/1881 Crich et a1. 118/124 X SHEET REMOVAL DEVICE Thisinvention relates to apparatus for fixing a toner image to a finalsupport sheet and, in particular, to means for facilitating the removalof a toner bearing support sheet from a heated pressure roll fusingmechamsm.

In the process of xerography, a light image of an original to be copiedis conventionally recorded in the form of a latent electrostatic imageupon a photosensitive plate and the latent image then rendered visibleby the application of a heat sensitive toner material. The visual imagecan be either fixed directly upon the photosensitive plate ortransferred from the plate to a sheet of final support material, such asplain paper or the like, and the image affixed thereto. One prevalentmethod of accomplishing image fixing is through means of a heat pressureroll technique wherein the toner bearing support material is passedthrough the nip of two cooperating pressure rolls with the image side ofthe support material contacting one of the roll surfaces which ismaintained at an elevated temperature. Sufficient energy is transferred,under pressure, from the heated roll surface to the image bearingsupport material to accomplish the desired image fixing. A typicalpressure roll fusing system of this type is disclosed in US. Pat. No.3,256,002 which issued in the name of Hudson.

As described in the above-noted Hudson patent, the outer surface of theheated roll is generally provided with a release agent which serves toprevent the toner images carried on the support sheet from offsettingfrom the sheet onto the fuser roll surface. Silicone based oils, whichpossess relatively low surface energies, have been found to be amaterial that is suitable for use in the heated roll fuser environment.A thin layer of oil is applied to the contact surface of the heated rollwhich interfaces between the roll surface and the toner images carriedon the support material. A low energy profile is thus presented to thetoner as it passes through the fuser nip which, under most conditions,prevents the toner from adhering to the heated fuser roll surface.Although the low surface energy oils generally act as a non-wettingfluid in regard to most support materials, it has been found that amechanical flowing of the release agent from the roll onto the supportmaterial will occur if an excess of oil is allowed to accumulate in aregion where it can come in contact with the copy sheet. Accordingly,the amount of oil applied to the roll surface is usually metered undercontrolled conditions to maintain a relatively thin coating of therelease agent upon the roll surface.

As the toner'image bearing support sheet passes through the nip of thefuser roll, the support sheet, because of the geometry of the system andthe forces involved, will most generally want to remain in contact withthe heated roll surface. As a result, the copy sheet is carried along onthe surface of the heated roll as the sheet passes beyond the fusing nipand some instrumentality, such as a stripper blade or the like, must beintroduced between the sheet and the roll surface to affect removal. Thesheet removal device, because it comes into contact with the thin layerof oil maintained on the heated roll surface, is capable of paddling oraccumulating an excess of oil at the point where the sheet is separatedfrom the roll surface. The trailing portion of the sheet, which is thenpulled through the puddle of excess oil, picks up the oil thus degradingthe quality of the copy produced.

A further difficulty associated with this type of mechanism is caused bytoner adhering to the pick off device. The heated toner, coming incontact with the pick off mechanism is in a highly tackified viscousstate and, as such, wants to stick to any surface it contacts. As aresult, the images on the copy sheet moving thereover will generallycling to the pick off mechanism causing image degradation and impede oreven stop the sheets movement.

It is therefore an object of the present invention to improve heatedpressure roll image fixing devices.

A further object of the present invention is to facilitate the removalof a support sheet from the surface of a heated image fixing roll.

Yet another object of the present invention is to eliminate supportsheet jams within a pressure roll image fixing system.

A still further object of the present invention is to provide anon-deleterious sheet removal device suitable for use in a pressure rollimage fixing apparatus.

Another object of the present invention is to remove a toner imagebearing support sheet from the surface of a heated fuser roll withoutharmfully disturbing the release agent carried on the fusing rollsurface or the toner images carried upon the support material.

These and other objects of the present invention are attained by meansof a sheet removal device which is adapted to move between the surfaceof an oil coated heated fuser roll and an image bearing support sheetcarried thereon the removal device having a cutting edge which is shapedto prevent oil from accumulating in and about the contact region, thesheet removal device being formed of a material which is incapable ofmechanically of chemically interacting with toner images brought incontact therewith thus preventing the toner from adhering to the contactsurface. Further means, operatively associated with the sheet removaldevice, are also provided to remove the blade from within the sheetcontact region upon the sensing of a support sheet jam condition wherebypotential damage to the fuser roll is averted.

For a better understanding of the present invention as well as otherobjects and further features thereof, reference is had to the followingdetailed description of the invention to be read in connection with theaccompanying drawings wherein:

FIG. 1 is a perspective view in partial section illustrating a heatedpressure roll image fixing assembly employing the sheet removalapparatus of the present invention;

FIG. 2 is an end view in partial section of the lower fuser roll of theassembly shown in FIG. 1 illustrating the sheet removal apparatus of thepresent invention positioned in an operative condition;

FIG. 3 is an end view in partial section of the lower fuser roll of theassembly illustrated in FIG. -1 showing the sheet removal apparatus ofthe present invention positioned in an inoperative condition;

FlG. 4 is a top plan view showing the contour of a sheet stripping bladeemployed in the apparatus of the present invention;

FIG. 5 is a partial end view in section of the lower fuser rollillustrated in FIG. 1 showing a second embodiment of the sheet removaldevice suitable for use in the present invention;

FIG. 6 is also a partial end view illustrating another embodiment of thepresent invention.

Referring now to FIG. I, there is shown a typical heat pressure rollfixing system utilizing the sheet removal apparatus of the presentinvention. This system is similar to that disclosed in regard to theabove-noted Hudson patent. A pair of co-acting fuser rolls, including alower heated roll 11 and an upper back up roll 12, are rotatably mountedwithin a support frame 13 and have drive means (not shown) operativelyassociated therewith for rotating the rolls at synchronous speeds in thedirection indicated. As disclosed by Hudson, one of the roll members, inthis particular case the bottom roll 12, is provided with an internalsource of heat energy and is arranged so that its outer surface contactsthe toner image bearing side of a copy sheet 15 as the sheet istransported through the nip of the fuser roll assembly. The lower orheated fuser roll 11 is formed of a resilient blanket 16, which isplaced over a copper core 17, and having a thin layer of relativelyabhesive material 18, as for example triflouroethylene, placedthereover. Running axially through the interior of the copper core is aquartz heating lamp I9 which functions to transfer sufficient energy tothe roll member so as to raise the surface temperature thereof to apredetermined operating level.

The upper or back up fuser roll 12 is made up of a relatively rigidcylindrical substrate 20, preferably being fabricated of a stainlesssteel, over which a relatively thick sleeve 21 of trifiouroethylene isfitted. In assembly, the two co-acting rolls are mounted in the frame sothat the lower resilient heated roll is deformed against the more rigidupper roll thus creating an extended nip therebetween through which thecopy sheet is passed during the fusing process. During passage of thesheet, sufficient pressure and heat energy is transferred from the fuserassembly to the copy sheet to affect the desired image fixing.

Although the present invention will be described with reference to theabove-noted pressure roll image fixing system, it should be clear to oneskilled in the art that the instant invention is not necessarily limitedor restricted in its usage to this particular fixing system and that itcan be similarly utilized in a wide variety of pressure roll fixingsystems presently known and used in the art.

In order to prevent the toner image carried by the final support sheetfrom being offset onto the heated roll surface, as the sheet is drawnthrough the fuser nip, the heated roll is provided with a layer of oilcontaining a release agent capable of preventing the toner image fromadhering to the heated roll surface. Silicone based oils have been foundto be a suitable release agent for this intended purpose. An oilapplicating mechanism, generally referenced 25, is positioned adjacentto the lower portion of the heated fuser roll as illustrated in FIG. I.An applicator wick 26 is mounted in the upper part of housing 27 and isarranged to contact the lower portion of the heated roll surface. Arotating oil metering cylinder 28 is located directly beneath the wickand serves to transport a regulated amount of oil from the housing sumpregion 29 upwardly into contact with the wick surface. Sufficient oil iscarried to the wick by the metering roll to allow the wick to apply tothe outer pe' riphery of the heated fuser roll a relatively thinhomogeneous coating of oil. The oil coating applied to the fuser rollsurface must be thick enough to act as an interface between the rollsurface and the copy sheet to prevent toner offsetting but yet must bethin enough to prevent wetting of the copy sheet as it moves through thefuser nip. For further information concerning this type of oil meteringsystem reference is had to US. Pat. No. 3,718,116.

As previously noted, the image bearing support sheet, as it passesthrough the nip of the fuser roll assembly, tends to remain in contactwith the lower heated pressure roll surface. As a consequence, someinstrumentality must be provided to effect the removal of the supportsheet from the roll surface after image fixing is accomplished. To thisend, a pair of pick off fingers 30 are mounted slightly downstream fromthe nip of the fuser roll assembly. The fingers are arranged to movebetween the lower fuser roll surface and the copy sheet in process. Thecopy sheet, as it leaves the fuser nip, is carried forward by the rolland thus caused to come into contact with the upper surface of thestripper fingers. The fingers, moving between the sheet and the roll,redirect the sheet along a second predetermined path of travel away fromthe roll thus effecting the desired separation.

Conventionally, when this type of sheet pick off device has heretoforebeen employed in a heated pressure roll fuser system, the pick off bladeelement invariably would doctor the oil carried on the heated rollsurface thus producing a puddle of excess oil to build up at the tip andtop face of each finger. This copious amount of oil, which isaccumulated within the sheet removal region, poses an ever presentdanger to the sheet in process supply because the amount of oil is suchthat mechanical offsetting of the oil to the sheet cannot be avoided.

The apparatus of the present invention, among other things, isspecifically designed to eliminate any harmful oil accumulations in andabout the sheet pick up region. Excessive oil build ups are prevented bythe present apparatus by first shaping the tip of the pick off finger topermit oil to flow around the blade and secondly by providing means forcollecting excess oil flowing over the top of the finger and carryingthe oil away from the region where it is capable of contacting thesupport sheet.

As illustrated in FIGS. 1, 2 and 4, the sheet removal apparatus of thepresent invention includes two bladelike fingers 31 which are pivotablymounted upon the free ends of pivot pins 32. The pivot pins, in turn,are anchored at one end in a vertical support member 34 which is securedto a horizontal tie bar 35. Each finger is provided with a cutting edge36 which is formed by the joinder of the top surface 38 and inclinesurface 39 formed in the body of the finger. The fingers are supportedin the assembly so that the inclined lower surface 39 thereon restsunder the influence of gravity upon the heated lower pressure rollsurface. The finger contacts the roll along a line of contact that istangent to the roll surface which is located about 0.001 inches backfrom the cutting edge of the finger.

As seen in FIG. 4, the cutting face of each finger is provided with anarcuate shape which permits the oil carried upon the heated roll surfaceto conveniently flow about each side of the fingers. The side rake inthe face of the finger is created by forming a radius at the tip of thefinger which is substantially normal to the top surface of the finger.It has been found that good flow characteristics can be obtained whenthe radius (r) formed in the finger is at least as great or greater thanthe radius (R) of the heated fuser roll.

It has also been found that the oil carried on the fuser roll, whenbrought into moving contact with the stripper fingers, will tend to moveor flow over the upper surface of the fingers. The oil, coming intocontact with the relatively cooler body portion of the finger, continuesto walk up the cooler surface via capillary action and where if leftunchecked, the oil will begin to build up in dangerous amounts. As canbe seen, therefore, shaping the cutting edge of the sheet strippingdevice will, not in itself, prevent an oil build up from occurringwithin or along the intended path of travel of a copy sheet as it isremoved from the fuser roll.

in order to prevent an excess of oil from building up on the top surfaceof the stripper fingers, a clear aperture 40 is formed in the main bodyof each finger directly behind the cutting edge into which the excessiveoil is capable of falling and being collected. Preferably, the openingshould be positioned so that the oil passing therethrough falls backinto contact with the fuser roll surface directly below the point whereit is removed by the finger tip. In this way, a continuous flow of oilis produced around the tip wherein the oil removed during the sheetstripping operation is put back on the roll surface in the depletedregions. As shown in FIG. 2, an absorptive pad 41 is mounted within theopening 40 which serves as an oil reservoir to store the oil soaccumulated. The pad also serves as a metering device for feeding oilback to the upper surface of the pick off fingers to wet the surfacethereof with a thin coating of oil for preventing toner from adhering tothe surface as the copy sheet is moved thereover. Oil pads formulated ofwool or of high density Dacron, having a relatively high oil retentioncapacity, have been found to be capable of metering oil back to thefinger surface via capillary action at a rate that will maintain a thinfilm of oil upon the top surface of the finger. It should be clear toone skilled in the art, however, that the present invention is notlimited or restricted to the above-named material and any suitablematerial capable of producing the desired results can be herein utilizedwithout departing from the teachings of the present invention.

A second embodiment illustrating another finger configuration is shownin FIG. 5. A recess or step 57 is formed in the top surface 58 of theblade-like finger 59 into which excessive oil flowing over the top ofthe blade is caused to drop thus preventing the oil from contacting themain body of the copy sheet as it moves thereover. As in the previousfinger configuration, an aperture 60 is also provided in the body of thefinger through which excessive oil collected in the recess can beexhausted from the system. Alternatively, the aperture 60 can be filledwith an absorbent pad 61 capable of collecting and storing excessive oildelivered thereto.

Referring to FIG. 6, there is illustrated another embodiment of a finger80 for controlling the puddling of oil within the sheet pick off region.The top surface of the finger 81 is stepped to provide a recess 82 intowhich oil moving over the blade is collected. Along both side walls ofthe finger there is provided an oil channel 83 for directing the oilcollected in the recess downwardly toward the bottom surface of thefinger. The oil collected within the recess 82 is directed intohorizontal gutters 85 formed in the top surface of the recess and isguided into the side wall channels 83. The bottom surface of the fingeris V-shaped in construction with the apex 84 of the V pointed at themoving surface of the fuser roll. In operation, the oil collected in therecess 82 is directed downwardly via the channel 83 and then moves alongthe bottom of the finger where it collects at the apex 84. Whensufficient oil is collected at the apex to overcome the surface energiesinvolved, the oil is released from the finger and falls into contactwith the roll surface thus automatically replenishing the oil supplythereon directly below the area wherein the blade acts to deplete theoil supply. A continuous flow of oil is thus established whereinsubstantially the same amount of oil is delivered back onto the roll asis removed by the action of the finger. The channel 83 can take almostany form. In practice it was found that a shallow groove machined in thefinger side wall would operate to establish the desired oil flow.Similarly, a protruding boss in the side walls also provides the sameresults.

To further prevent toner from adhering from the top surface of thefinger, as a copy sheet is drawn thereover, the fingers are preferablyconstructed of a material that will neither mechanically or chemicallyinteract with the toner in a manner to cause the toner to adhere to thefinger surface. Such materials, as aromatic polyesters, as for example,Econol as manufactured by the Carborumbum Co., of Sanbornn, N.Y., whichare loaded with a triflouroethylene filler; amide imides, as for exampleAmoco Al-llL 4 as supplied by the Amoco Chemical Company of Syemor,lnd., which are loaded with a graphite and triflouroethylene filler;polymides, as for example Vespel as manufactured by the duPont Co.,which are coated with a layer of triflouroethylene have all been foundto exhibit non-adhering characteristics to toner and are well suited foruse in the construction of the sheet removal fingers.

Similarly, it has been found that by keeping the sheet contactingsurface of the fingers at a temperature that is relatively cooler thanthe fixing temperature of the toner material, adhesion of the toner tothe finger can also be inhibited. It is believed that the relatively hottoner leaving the fuser roll will rapidly pass from a tacky semi-liquidstate into a more stable solidified state upon contacting the coolerblade surface thus placing the toner in a non-offsetting condition. Afinger, which is constructed of a metal having a high coefficient ofthermal conductivity, such as aluminum or the like, and which is coatedwith a thin layer of triflouroethylene has been found to work well inthe practice of the present invention. In this embodiment, the main bodyof the fingers should have sufficient mass so that it acts as arelatively large heat sink in regard to the blade edge region whereby aheat build up at the cutting edge is rapidly dissipated into the massivebody of the blade. By maintaining the finger surface temperature at orbelow F, satisfactory toner release characteristics can be obtained.

It should be further noted that this type of blade has the capability ofworking well in conjunction with dry fuser rolls as well as with thosecoated with a release agent.

A further safety feature is also provided for in the present apparatusin order to protect the heated roll surface from being abraided orotherwise harmed by the sheet stripping fingers. When, for reasonsbeyond the control of the present sheet stripping apparatus, a copysheet becomes misaligned or otherwise inadvertently becomes attached orotherwise enmeshed with the sheet removal fingers, the fingers arecaused, due to the forces involved, to work harder against the rollsurface. This, in turn, causes the blade edges of the fingers to diginto the generally sensitive roll surface. Under extreme conditions, theedge of the blade can cause sufficient damage to the roll surfacewhereby the roll must be replaced within the fuser assembly.

As illustrated in FIGS. 2 and 3, the body of each finger is supportedupon the pivot pin 32 by means of a spring clip 70. Both ends of theclip are anchored in the end wall 71 of the finger with the extendedbody of the clip being turned so that it is carried within an elongatedopening 73 provided for in the main body of the finger. A circulardetent 75 (FIG. 3), capable of engaging the pivot pin 32, is formed inthe clip which serves to support the clip in an operative position uponthe pin in the manner shown in FIG. 2. Upon the occurrence of a sheetjam condition, whereby the finger is caused to exert undue pressureagainst the roll surface, the tinger is forced back against the holdingpressure of the pivot pin with sufficient pressure to cause the pin tobe released from the detent. The finger is thus permitted to fall awayfrom the roll surface to an inoperative condition as illustrated in FIG.3. It should be clear that the detent release pressure of the spring isset at a point whereby the pressure required to release the finger isbelow that at which the fingers could harm the roll surface. In thissense, the spring apparatus has the ability to sense the impendingoccurrence of a jam condition and automatically take appropriatecorrective action before any damage can be sustained by the rollsurface.

While this invention has been described with reference to the structuredisclosed herein, it is not necessarily confined to the details as setforth and this application is intended to cover such modifications orchanges as may come within the scope of the following claims.

What is claimed is:

1. In a reproduction machine wherein a developed electrostatic image istransferred to a suitable image bearing support sheet and permanentlyaffixed thereto by heat-pressure means including a heated pressure roll,the improvement comprising:

means applying a release agent coating to the heated pressure roll;

a blade-like element having a cutting edge formed along one sidethereof; and

means for supporting said blade-like element in close proximity to anupper portion of the heated pressure roll with the cutting edge of theblade in a position to strip a support sheet moving therefrom, saidblade having a recess formed therein behind the cutting edge thereof andextending through the blade, said recess overlying a lower portion ofthe heated pressure roll whereby release agent removed from the roll bysaid blade is returned to the roll.

2. The apparatus of claim 1 wherein the cutting edge of said blade has aradius formed therein that is greater than the radius of the fuser roll.

3. The apparatus of claim 2 wherein said recess is a aperture formed inthe body of the blade behind the cutting edge thereon.

4. The apparatus of claim 3 wherein said aperture is filled with amaterial capable of absorbing said removed oil.

5. The apparatus of claim 1 wherein said cutting edge contacts the rollsurface along a contact line that is tangent to the surface of saidroll.

6. The apparatus of claim 1 wherein the blade has means operativelyassociated therewith for removing the blade from contacting said rollwhen the contact force between the roll and the blade exceeds apredetermined pressure.

7. The apparatus of claim 1 wherein said blade is formed of an aromaticpolyester filled with triflouroethylene.

8. The blade of claim 1 wherein said blade is formed of a polymide whichis filled and covered with triflouroethylene.

9. The blade of claim 1 wherein said blade is formed of an amide-imide.

10. The apparatus of claim 1 wherein said blade if formed of a metalhaving relatively high thermal conductivity.

11. The apparatus of claim 10 wherein said metallic blade is coated witha layer of triflouroethylene.

12. The apparatus of claim 4 wherein said absorbent material comprisesan oil reservoir holding a quantity of said removed oil which is meteredto the blade surface by capillary action.

13. The apparatus of claim 12 wherein said absorbent material comprisesa high density wick which is embedded below the sheet contacting surfaceof said blade.

14. The apparatus of claim 1 wherein said recess is a channel runningalong at least one side wall of said blade.

15. The apparatus of claim 1 wherein said recess is an embossed ridgerunning along at least one side wall of said blade.

1. IN A REPRODUCTION MACHINE WHEREIN A DEVELOPED ELECTTROSTATIC IMAGE ISTRANSFERRED TO A SUITABLE IMAGE BEARING SUPPORT SHEET AND PERMANENTLYAFFIXED THERETO BY HEAT-PRESSURE MEANS INCLUDING A HEATED PRESSURE ROLL,THE IMPROVEMENT COMPRISING: MEANS APPLYING A RELEASE AGENT COATING TOTHE HEATED PRESSURE ROLL; A BLADE-LIKE ELEMENT HAVING A CUTTING EDGEFORMED ALONG ONE SIDE THEREOF; AND MEANS FOR SUPPORTING SAID BLADE-LIKEELEMENT IN CLOSE PROXIMITY TO AN UPPER PORTION OF THE HEATED PRESSUREROLL WITH THE CUTTING EDGE OF THE BLADE IN A POSITION TO STRIP A SUPPORTSHEET MOVING THEREFROM, SAID BLADE HAVING A RECESS
 2. The apparatus ofclaim 1 wherein the cutting edge of said blade has a radius formedtherein that is greater than the radius of the fuser roll.
 3. Theapparatus of claim 2 wherein said recess is a aperture formed in thebody of the blade behind the cutting edge thereon.
 4. The apparatus ofclaim 3 wherein said aperture is filled with a material capable ofabsorbing said removed oil.
 5. The apparatus of claim 1 wherein saidcutting edge contacts the roll surface along a contact line that istangent to the surface of said roll.
 6. The apparatus of claim 1 whereinthe blade has means operatively associated therewith for removing theblade from contacting said roll when the contact force between the rolland the blade exceeds a predetermined pressure.
 7. The apparatus ofclaim 1 wherein said blade is formed of an aromatic polyester filledwith triflouroethylene.
 8. The blade of claim 1 wherein said blade isformed of a polymide which is filled and covered with triflouroethylene.9. The blade of claim 1 wherein said blade is formed of an amide-imide.10. The apparatus of claim 1 wherein said blade if formed of a metalhaving relatively high thermal conductivity.
 11. The apparatus of claim10 wherein said metallic blade is coated with a layer oftriflouroethylene.
 12. The apparatus of claim 4 wherein said absorbentmaterial comprises an oil reservoir holding a quantity of said removedoil which is metered to the blade surface by capillary action.
 13. Theapparatus of claim 12 wherein said absorbent material comprises a highdensity wick which is embedded below the sheet contacting surface ofsaid blade.
 14. The apparatus of claim 1 wherein said recess is achannel running along at least one side wall of said blade.
 15. Theapparatus of claim 1 wherein said recess is an embossed ridge runningalong at least one side wall of said blade.